Path search device and method, and array antenna reception device using the same

ABSTRACT

There are provided a path search apparatus and method and array antenna unit using them which receive signals of a DS-CDMA scheme from an array antenna unit including a plurality of antenna elements and detect multipath timings. In a signal receiving system having a plurality of array antenna units ( 141, 142 ), a delay profile is combined for each of antenna elements ( 11 - 16 ), and path detection is performed using the combined output, thereby allowing higher-precision and higher-speed path detection. In addition to a delay profile for each antenna element, delay profiles may be combined across array antenna units (diversity branches). When beams are to be formed in a searcher section ( 44 ), delay profiles are combined for respective beams facing in a single direction across the array antenna units.

This application is based upon and claims priority under U.S.C. §119from PCT Application No. PCT/JP03/06111, filed May 16, 2003, at leastentire content are incorporated herein by reference, and Japanese PatentApplication No. 2002-147077 filed May 22, 2002, at least entire contentare incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a path search apparatus and method andan array antenna receiving apparatus using them and, more particularly,to a path search system which receives signals of a DS-CDMA (DirectSpread-Code Division Multiple Access) scheme from an array antenna unitcomprising a plurality of antenna elements and detects multipathtimings.

BACKGROUND OF THE INVENTION

A receiving apparatus of a mobile communication system using a DS-CDMAscheme now use a diversity antenna. In a diversity antenna unit, todecrease correlation between antenna elements, antennas are arrangedsuch that antenna elements 1 and 2 have a large interval D1, as shown inFIG. 1 (e.g., an interval of several λ; λ is a signal wavelength). Sincethe correlation is small, one antenna element can often receive signalsat a high level even when the reception level of the other antennaelement decreases due to fading. The probability of degradation inreception quality can be reduced more than a case wherein fading wavesare received using one antenna. A reception scheme using a diversityantenna unit, however, is directly influenced by interference waves ifpresent.

As a technique for reducing degradation in quality due to interferencewaves, there is available a reception technique using an array antennaunit. In this array antenna unit, antennas are arranged such that aplurality of antenna elements 3 to 5 have a small interval D2 (aninterval of about λ/2), as shown in FIG. 2. By multiplying a signalreceived by each antenna element by amplitude and phase weights, thedirectivity pattern (beam) of each antenna can equivalently be formed.If an area is divided by a plurality of beams thus formed, the influenceof interference waves in a direction different from that of a desiredwave can be suppressed.

Since the array antenna unit has the small element interval D2, as shownin FIG. 2, correlation between the antenna elements becomes extremelylarge. For this reason, a decrease in reception level due to fadinginfluences all antenna elements constituting the array antenna unit, anddegradation in reception quality cannot be compensated. If an intervalbetween antenna elements is increased, no ideal beam can be formed, andthe primary object, i.e., suppression of interference waves cannot beattained.

As a scheme which covers up disadvantages and exploits advantages of adiversity antenna unit and array antenna unit, a technique that pertainsto an antenna unit is disclosed in, e.g., WO 00/03456. The antenna unithas a plurality of array antenna units each comprising a plurality ofantenna elements 3 to 5 or 6 to 8, as shown in FIG. 3, and the pluralityof array antenna units are separated from each other such thatcorrelation between them can be neglected.

However, in the description of a receiving apparatus of a DS-CDMAcommunication scheme which has a plurality of array antenna units eachcomprising the plurality of antenna elements 3 to 5 or 6 to 8, as shownin FIG. 3, there is neither reference to nor implication of a pathsearch scheme which detects multipath timings. Thus, high-precision andhigh-speed path search is demanded for a receiving apparatus having anantenna unit arrangement as shown in FIG. 3.

An example of the arrangement of a receiving apparatus in a mobilecommunication system of a CDMA scheme using a conventional diversityantenna unit will be described with reference to FIG. 4.

In searcher sections 401 a and 401 b of a conventional diversity antennareceiving apparatus in FIG. 4, detection of a synchronization chiptiming (path detection) between a spreading code and a spread signal asa received signal is performed independently for each antenna. Pathcombining means 61 a and 61 b and an antenna combining (diversitycombining) means 91 perform RAKE combination reception using the pathtiming information.

The prior art will be described in detail with reference to FIG. 4. InFIG. 4, antennas 11 a and 11 b are equivalent to the diversity antennas1 and 2 shown in FIG. 1. Signals received by the antennas 11 a and 11 bare frequency-converted into intermediate-frequency (IF band) signals inradio receivers 21 a and 21 b and are amplified. After the amplifiedsignals are detected to I/Q channel baseband signals using quadraturedetection, they are converted into digital signals by A/D converters.The outputs from the radio receivers 21 a and 21 b are sent out tofinger sections 301 a and 301 b and searcher sections 401 a and 401 b.

In the searcher sections 401 a and 401 b, correlation calculating means101 a and 101 b calculate the code correlation values of desired wavesignals contained in received signals at a plurality of chip timings.Correlation value averaging means 111 a and 111 b average correlationvalues output at a single chip timing from the correlation calculationmeans 101 a and 101 b for a predetermined period of time and output peakcorrelation values and delay profiles having undergone noise-levelsmoothing. The delay profiles generated by the correlation valueaveraging means 111 a and 111 b are input to path timing detecting means131 a and 131 b. The path timing detecting means 131 a and 131 b detectpeaks from the combined delay profiles and notify the finger sections301 a and 301 b of synchronization chip timings corresponding to thedetected peaks.

Each of the finger sections 301 a and 301 b has fingers corresponding innumber to paths to be demodulated and has demodulating means 51 a to 53a and 51 b to 53 b corresponding in number to the fingers. Each fingeris allocated to one path (synchronization chip timing). The demodulators51 a to 53 a and 51 b to 53 b demodulate signals at the synchronizationchip timings and output the demodulated signals to the path combiningmeans 61 a and 61 b. The path combining means 61 a and 61 b combine thedemodulation results for the respective paths into antenna outputs,which are supplied to and combined by a diversity combining means 91.After that, the combination result is sent to a decoder (not shown).

The example of a receiving apparatus in a mobile communication system ofa CDMA scheme using a conventional diversity antenna has been described.High-precision and high-speed path search is demanded for this receivingapparatus.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of theabove-mentioned circumstances, and has as its object to provide a pathsearch apparatus and method which can perform high-precision andhigh-speed path search, and an array antenna receiving apparatus usingthem.

To achieve the above-mentioned object, according to the presentinvention, there is provided a path search apparatus which receives asignal of a CDMA scheme by an array antenna unit including a pluralityof antenna elements and detects a multipath timing, characterized bycomprising a plurality of array antenna units, delay profile combiningmeans for combining delay profiles for respective antenna elements inthe plurality of array antenna units, and path timing detecting meansfor detecting path timings of respective outputs from the delay profilecombining means.

According to the present invention, the delay profile combining means isprovided for each of the plurality of array antenna units and isarranged to combine the delay profiles for the antenna elements in thearray antenna unit.

According to the present invention, the delay profile combining means isarranged to collectively combine the delay profiles for the respectiveantenna elements in the plurality of array antenna units.

According to the present invention, there is provided a path searchapparatus further comprising beam forming means for forming a beam usingas an input a signal received by each antenna element in each of theplurality of array antenna units, wherein the delay profile combiningmeans is arranged to combine delay profiles for respective beams facingin a single direction across the plurality of array antenna units. Thebeam forming means in the path search apparatus has multiplying meansfor multiplying an output from each antenna element by a predeterminedmultiplication value.

To achieve the above-mentioned object, according to the presentinvention, there is provided a path search method of receiving a signalof a CDMA scheme by a plurality of array antenna units each including aplurality of antenna elements and detecting a multipath timing,characterized by including the delay profile combining step of combiningdelay profiles for respective antenna elements in the plurality of arrayantenna units, and the path timing detecting step of detecting pathtimings of respective outputs in the delay profile combining step.

According to the present invention, in the delay profile combining step,a delay profile for each antenna element is combined for each of theplurality of array antenna units.

According to the present invention, in the delay profile combining step,the delay profiles for the respective antenna elements in the pluralityof array antenna units are collectively combined.

According to the present invention, there is provided a path searchmethod characterized by further comprising the beam forming step offorming a beam using as an input a signal received by each antennaelement in each of the plurality of array antenna units, wherein in thedelay profile combining step, delay profiles are combined for respectivebeams facing in a single direction across the plurality of array antennaunits. The beam forming step in the path search method comprises amultiplying step of multiplying an output from each antenna element by apredetermined multiplication value.

To achieve the above-mentioned object, according to the presentinvention, there is provided an array antenna receiving apparatuscharacterized by comprising any one of the above-mentioned path searchapparatuses, and demodulating means, provided for each of the pluralityof array antenna units, for demodulating a signal received by eachantenna element in the array antenna unit on the basis of a path timingdetected by the path search apparatus.

According to the present invention, there is provided an array antennareceiving apparatus characterized by further comprising weighting means,provided for each of the plurality of antenna units, for weightingdemodulation outputs from the respective antenna elements by adaptivecontrol, and combining means for RAKE-combining outputs from theweighting means.

The operation of the present invention will be described. In a signalreceiving system having a plurality of array antenna units, delayprofiles are combined for respective antenna elements, and pathdetection is performed using the combined output, thereby allowinghigher-precision and higher-speed path detection than a conventionalpath search scheme. In a signal receiving system having a plurality ofarray antenna units, delay profiles are combined not only for respectiveantenna elements but also across array antenna units (diversitybranches). Path detection is performed using the combined output,thereby allowing high-precision and high-speed path detection. In asignal receiving system having a plurality of array antenna units, whenbeams are to be formed by a searcher section, delay profiles arecombined for respective beams facing in a single direction across arrayantenna units (diversity branches), and path detection is performedusing the combined output, thereby allowing high-precision andhigh-speed path detection.

As described above, according to the present invention, path search canbe performed at high precision and high speed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an antenna layout example using a diversityantenna unit;

FIG. 2 is a view showing an antenna layout example using an arrayantenna unit;

FIG. 3 is a view showing an antenna layout example using a combinationof a diversity antenna unit and an array antenna unit;

FIG. 4 is a block diagram showing an example of a receiving apparatus ofa CDMA scheme which uses conventional diversity antenna units;

FIG. 5 is a block diagram of the first embodiment of a receivingapparatus according to the present invention;

FIG. 6 is a block diagram of the second embodiment of a receivingapparatus according to the present invention; and

FIG. 7 is a block diagram of the third embodiment of a receivingapparatus according to the present invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments will be described with reference to theaccompanying drawings to explain the present invention in detail.

The first embodiment of the present invention will be described withreference to FIG. 5.

FIG. 5 shows, as an example, a receiving apparatus which has two arrayantenna units each consisting of three antenna elements. In the presentinvention, however, the number of antenna elements or array antennas isnot limited to that shown in FIG. 5. The present invention is alsoeffective for an arbitrary number of antenna elements or array antennas.The interval between antenna elements is about half the wavelength ofcarrier waves, and an interval D1 between array antenna units is set toa distance (several λ) which allows to sufficiently reduce thecorrelation.

The first embodiment has an array antenna unit 141 comprising antennaelements 11 to 13, and an array antenna unit 142 comprising antennaelements 14 to 16, as shown in FIG. 5. The first embodiment includesradio receivers 21 to 26 which convert RF signals from the antennaelements into digital baseband signals, searcher sections 41 and 42which detect the path positions (synchronization chip timings) of therespective array antenna units (diversity branches), finger sections 31and 32 which demodulate signals at the timings detected by the searchersections, calculate weights using a known adaptive algorithm such asMMSE (Minimum-Mean-Squared-Error), and multiply the signals by theweights to form beams, path combining means 81 and 82 which combine thedemodulation results from the fingers, and a diversity combining means91 which combines the demodulation results from the branches.

The searcher section 41 includes correlation calculating means 101 to103 corresponding in number to the antenna elements, correlation valueaveraging means 111 to 113 for averaging correlation results of theantenna elements and generate delay profiles, a delay profile combiningmeans 121 for adding and combining the delay profiles, and a path timingdetecting means 131 for detecting a synchronization chip timing from thecombined delay profile. The other searcher section 42 includes the samecomponents.

The finger section 31 has a plurality of fingers, each of which includesdemodulating means 51 to 53 corresponding in number to the antennaelements, a weight multiplying means 61, and an adaptive control means71. The other finger section 32 includes the same components.

The operation of the first embodiment will be described next. Receiversconnected to the array antenna unit 141 and those connected to the arrayantenna unit 142 have the same arrangement. Thus, the receiversconnected to the array antenna unit 141 will be exemplified below.

RF signals received by the antenna elements 11 to 13 are sent to theradio receivers 21 to 23, respectively. After the RF signals arefrequency-converted into intermdiate-frequency (IF band) signals in theradio receivers 21 to 23, they are amplified by automatic gainamplifiers. The amplified signals are detected to I/Q channel basebandsignals using quadrature detection and are converted into digitalsignals by A/D converters. The outputs from the radio receiver 21 to 23are sent to the finger section 31 and searcher section 41.

In the searcher section 41, the correlation calculating means 101 to 103calculate the code correlation values of desired wave signals containedin received signals at a plurality of chip timings for the respectiveantenna elements. The correlation value averaging means 111 to 113average correlation values output at a single chip timing from thecorrelation calculating means 101 to 103 for a predetermined period oftime and output peak correlation values and delay profiles havingundergone noise-level smoothing.

The delay profiles for the respective antenna elements generated by thecorrelation value averaging means 111 to 113 are combined at a singlechip timing by the delay profile combining means 121 into a combineddelay profile. The path timing detecting means 131 detects a pluralityof peaks from the combined delay profile and notifies the finger section31 of synchronization chip timings corresponding to the detected peaks.

The finger section 31 has fingers corresponding in number to paths to bedemodulated. One of them has the demodulating means 51 to 53corresponding in number to the antenna elements. Each finger isallocated to one path (synchronization chip timing). The demodulatingmeans 51 to 53 demodulate signals at the synchronization chip timingsand output the demodulated signals to the weight multiplying means 61.The weight multiplying means 61 multiplies the demodulation results byweights calculated by the adaptive control means 71 and supplies themultiplication results to the path combining means 81.

The path combining means 81 combines the demodulation results for therespective paths into one output from the array antenna unit 141 andoutputs it to the diversity combining means 91.

The diversity combining means 91 combines an output result from thearray antenna unit 141 and an output result similarly obtained from thearray antenna unit 142 and sends the combination result to a decoder(not shown).

According to the first embodiment, the level of noise contained in adelay profile is averaged and reduced, and peaks become prominent.Synchronization chip timings can be detected at high precision. Theimplementation of peak detection precision of the same level as that ofa conventional scheme makes it possible to shorten the averaging time ineach of the correlation value averaging means 111 to 116. In otherwords, synchronization chip timings can be detected at high speed, andthe capability of following up any variation in synchronization chiptiming of a multipath wave generated upon movement of a terminal can beimproved.

Generally, the peak level of a correlation value varies independentlyunder the conditions for antenna diversity in which the intervalsbetween antenna units are much longer than the wavelength of carrierwaves. The synchronization chip timings are considered to besubstantially equal to each other. Under the circumstances, the secondembodiment of the present invention will propose a receiver which alsocombines delay profiles across two array antenna units constitutingbranches.

FIG. 6 shows an example of the arrangement of a receiver indicative ofthe second embodiment of the present invention. The same referencenumerals in FIG. 6 denote the same parts as those in FIG. 5.

In FIG. 6, a delay profile combining means 123 does not output a resultfor each diversity branch and collectively combines the delay profilesfor all the antenna elements in both the branches to output thecombination result to a path timing detecting means 131. The path timingdetecting means 131 detects a plurality of peaks from the combined delayprofile and notifies finger sections 31 and 32 in the branches ofsynchronization chip timings for the respective detected peaks. Theremaining arrangement is the same as that in FIG. 5, and a descriptionthereof will be omitted. Note that reference numeral 43 denotes asearcher section in FIG. 6.

According to the second embodiment, synchronization chip timings can bedetected more precisely than the first embodiment shown in FIG. 5. Ifpeak detection precision only needs to be the same level as that of aconventional scheme, the second embodiment can detect synchronizationchip timings at higher speed than the first embodiment.

The present invention is also effective in forming beams by a searchersection. For an example, FIG. 7 shows, as the third embodiment, thearrangement of a receiving apparatus which forms a multibeam of threebeams for each diversity branch by a searcher section.

A multibeam can suppress interference waves from a direction differentfrom that of a desired wave by dividing a cover area for a plurality ofbeams using fixed weights. The details of this multibeam are disclosedin Japanese Unexamined Patent Publication No. 2001-345747, and adescription thereof will be omitted.

In FIG. 7, the same reference numerals denote the same parts as those inFIGS. 5 and 6. Referring to FIG. 7, weight multiplying means 63 and 64are added to a searcher section 44. Correlation calculating means 101 to103 and 104 to 106 calculate correlation values for respective antennaelements. Weight multiplying means 63 and 64 of the respective arrayantenna units multiply the correlation values by predetermined fixedamplitude weights and phase weights. The correlation values for theantenna elements are converted into correlation values for beams.

Correlation value averaging means 111 to 113 and 114 to 116 average thecorrelation values for the beams so as to output delay profiles for therespective beams. Delay profile combining means 124 to 126 combine beamsfacing in a single direction across the diversity branches at a singlechip timing and generate respective combined delay profiles for threebeams. A path timing detecting means 132 detects a plurality of peaksfrom the combined delay profile for the three beams and notifies fingersections 31 and 32 in both the diversity branches of synchronizationchip timings for the beams detected.

According to the third embodiment, when a searcher section is to formbeams, synchronization chip timings can be detected at high precisionand high speed. Note that the number of multibeams is not limited to aspecific one.

1. A path search apparatus which receives a signal of a CDMA scheme byan array antenna unit including a plurality of antenna elements anddetects a multipath timing, characterized by comprising: a plurality ofarray antenna units; delay profile combining means for combining delayprofiles for respective antenna elements in said plurality of arrayantenna units; and path timing detecting means for detecting pathtimings of respective outputs from said delay profile combining means.2. A path search apparatus according to claim 1, characterized in thatsaid delay profile combining means is provided for each of saidplurality of array antenna units to combine the delay profiles for theantenna elements in said array antenna unit.
 3. A path search apparatusaccording to claim 1, characterized in that said delay profile combiningmeans collectively combines the delay profiles for the respectiveantenna elements in said plurality of array antenna units.
 4. A pathsearch apparatus according to claim 1, characterized by furthercomprising beam forming means for forming a beam using as an input asignal received by each antenna element in each of said plurality ofarray antenna units, wherein said delay profile combining means combinesdelay profiles for respective beams facing in a single direction acrosssaid plurality of array antenna units.
 5. A path search apparatusaccording to claim 4, characterized in that said beam forming means hasmultiplying means for multiplying an output from each antenna element bya predetermined multiplication value.
 6. A path search method ofreceiving a signal of a CDMA scheme by a plurality of array antennaunits each including a plurality of antenna elements and detecting amultipath timing, characterized by including: the delay profilecombining step of combining delay profiles for respective antennaelements in the plurality of array antenna units; and the path timingdetecting step of detecting path timings of respective outputs in thedelay profile combining step.
 7. A path search method according to claim6, characterized in that in the delay profile combining step, a delayprofile for each antenna element is combined for each of the pluralityof array antenna units.
 8. A path search method according to claim 6,characterized in that in the delay profile combining step, the delayprofiles for the respective antenna elements in the plurality of arrayantenna units are collectively combined.
 9. A path search methodaccording to claim 6, characterized by further comprising the beamforming step of forming a beam using as an input a signal received byeach antenna element in each of the plurality of array antenna units,wherein in the delay profile combining step, delay profiles are combinedfor respective beams facing in a single direction across the pluralityof array antenna units.
 10. A path search method according to claim 9,characterized in that the beam forming step comprises a multiplying stepof multiplying an output from each antenna element by a predeterminedmultiplication value.
 11. An array antenna receiving apparatuscharacterized by comprising a path search apparatus defined in any oneof claims 1 to 5, and demodulating means, provided for each of theplurality of array antenna units, for demodulating a signal received byeach antenna element in the array antenna unit on the basis of a pathtiming detected by the path search apparatus.
 12. An array antennareceiving apparatus according to claim 11, characterized by furthercomprising weighting means, provided for each of said plurality ofantenna units, for weighting demodulation outputs from the respectiveantenna elements by adaptive control, and combining means forRAKE-combining outputs from said weighting means.